[exim] Exim 4.90.1: when sending mail, tries using A record…

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Author: Konstantin Boyandin
Date:  
To: exim-users@exim.org
Subject: [exim] Exim 4.90.1: when sending mail, tries using A record instead of MX
Hello,

Having a grave problem with recently compiled Exim 4.90.1 (running on
Ubuntu 16.04 64bit).

Primary domain: example.com

In /etc/aliases:

user:    user1@???,user2@???

When I run command like

exim -bt user@???

Exim prints correct MX records for every particular address the above
recipient forwards mail to. However, when I try actually send message to
the above, I see something like below in main.log:

2018-03-19 20:46:59 1exv5t-0003k7-NV ** user1@???
<user@???> R=dnslookup T=remote_smtp H=example.net [69.73.xx.xx]
X=TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256 CV=no: SMTP error from remote
mail server after RCPT TO:<user1@???>: 550-Please turn on SMTP
Authentication in your mail client.\n550-mail.example.com
(mail2016.example.com) [52.45.xx.xx]:49156\n550 is not permitted to
relay through this server without authentication.

(attempts to send mail to A records instead of any of MX)

DNS lookup router is pretty much standard:

dnslookup:
  driver = dnslookup
  domains = ! +local_domains
  transport = remote_smtp
  ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
  no_more

The host in A record doesn't process incoming mail for the domain in
question (in the above sample, example.net), thus delivery fails.

The above doesn't happen if I use Exim 4.87, and happens quite often if
I use 4.90.1

Is it a known issue? DNS resolver works without problem, I checked that
before sending yet another mail that failed in the above manner.

I would appreciate pieces of advice on how to handle this. Thank you.

Beat regards,
Konstantin